Method and Apparatus for a Self-Cleaning Filter

ABSTRACT

A method and apparatus for removing fine particulate matter from a fluid stream without interrupting the overall process or flow. The flowing fluid inflates and expands the flexible filter, and particulate is deposited on the filter media while clean fluid is permitted to pass through the filter. This filter is cleaned when the fluid flow is stopped, the filter collapses, and a force is applied to distort the flexible filter media to dislodge the built-up filter cake. The dislodged filter cake falls to a location that allows undisrupted flow of the fluid after flow is restored. The shed particulate is removed to a bin for periodic collection. A plurality of filter cells can operate independently or in concert, in parallel, or in series to permit cleaning the filters without shutting off the overall fluid flow. The self-cleaning filter is low cost, has low power consumption, and exhibits low differential pressures.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/694,156, filed Jun. 28, 2005. This application is also related toU.S. patent application Ser. No. ______, filed Jun. 28, 2006 (AttorneyDocket No. 026353-000300US). The entire contents of each of theseapplications are incorporated herein by reference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of SBIR ContractNo. DE-FG02-03ER83630 and SMB Contract No. ZDH-9-29047-01, both awardedby the U.S. Department of Energy.

BACKGROUND OF THE INVENTION

Embodiments of the present invention relate to a filter apparatus andmethod, and more particularly to self-cleaning filters for removingrelatively fine particulate material from a fluid stream.

Many fluid streams contain particulate matter, and it is often desirableto separate this particulate matter from the fluid stream. If notseparated, the particulate matter may degrade product quality,efficiency, reduce performance, or even cause severe damage tocomponents within the system.

Many types of filters have been designed for the purpose of removingparticulate matter from fluid streams. Such filters have typicallyincluded a filter element designed to screen the particulate material.However, the particulate material often becomes entrapped in the filterelement. As the quantity of particulate material, often referred to asfilter cake, collects on the filter element, the pressure drop thatoccurs across the filter element increases. A pressure drop across thefilter element of sufficient magnitude can significantly reduce fluidflow at which point the filter element must be periodically cleaned, orreplaced with a new filter. Often, this is done manually by removing thefilter element and cleaning the filter before reinstalling it back inthe system. Manual cleaning is a time consuming operation as it involvessignificant disassembly and re-assembly. It also requires taking theprocess off line. Manual cleaning can also be a dirty one, with thepotential for dislodging hazardous, or toxic, particles that can beinhaled or ingested. It can also be a dangerous operation, if the fluidis flammable or toxic.

To minimize manual operations, filters have been designed to accomplishcontinuous self-cleaning. However, filters that use back pulsing todislodge materials or blades to scrape off caked particulate are oftenvery intricate and costly mechanisms. Some filters are cleaned withsprayed fluids, such as water or air to remove the particulates oftenresulting in the need to dispose of a large fluid volume ofcontaminated, hazardous matter. Moreover, many current approachesrequire extreme pressures or forces to dislodge caked particulate fromthe filter.

What is needed are filter systems and methods that do not generateunwanted hazardous matter, and that able to remove particulates from afluid stream in a way that is relatively simple, reliable, flexible,easy to manufacture, that supports long-term operation, is easy tomaintain, and is self-cleaning. Relatedly, there continues to be a needfor filters that can be operated as one of a plurality of filters, andthat can operate either independently of other filters or in concertwith other filters. Embodiments of the present invention address atleast some of these needs.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provide techniques for removingfilter cake from a filter media in a very gentle and efficient manner.Moreover, embodiments are well suited for use in rural areas, as well asin developing countries, and often do not involve or minimize dependenceupon outside power sources. These approaches minimize the need forrepair and maintenance of such ancillary equipment. In some embodiments,filters provide a large surface area available for filtering thatincreases and does not make contact with any solid surface duringfiltration, thus making all of the filter's surface area usable. Filterembodiments provided herein often require no bag supports, scrapers,brushes, or nozzles to dislodge the filter cake.

In a first aspect, embodiments of the present invention encompass aprocess for removing a particulate from a fluid stream. The processincludes flowing a fluid stream containing a particulate through a fluidpermeable, flexible filter, expanding the filter and depositing theparticulate on an interior surface of the expanded filter, discontinuingthe flow of the fluid stream through the filter, collapsing the filterto distort the interior surface, and dislodging the particulate from thedistorted interior surface of the filter. In some cases, expanding thefilter can include creating or increasing a pressure differential acrossthe filter. Collapsing the filter can include removing or reducing thepressure differential across the filter. In some cases, expanding thefilter can include extracting an energy from the fluid stream andstoring the energy in a mechanical form. Collapsing the filter caninclude releasing the stored mechanical energy. In some aspects, flowingthe fluid stream includes controlling the fluid stream with a fluidcontrol means disposed upstream of the filter. In some aspects, flowingthe fluid stream can include controlling the fluid stream with a fluidcontrol means disposed downstream of the filter. The fluid control meanscan include, for example, a valve, a pump, a compressor, or a blower.

In another aspect, embodiments of the present invention encompass aself-cleaning filter apparatus for removing a particulate from a fluidstream. The filter apparatus can include a fluid-permeable, flexiblefilter having an expanded state and an inverted state. The expandedstate can be adapted to capture the particulate on an interior surfaceof the filter when receiving the fluid stream therethrough, and theinverted state can be adapted to dislodge the particulate from theinterior surface. The apparatus can also include a force meansconfigured to apply a force to the filter sufficient to convert thefilter from the expanded state to the inverted state. In some cases, theforce means is configured to extract an energy from the flowing fluidstream as it passes through the filter, to store the energy in amechanical form, and to release the stored mechanical energy to applythe force to the filter. The filter can be coupled with a tube sheet. Insome cases, the filter is free of any physical support structure, otherthan a tube sheet or a force means. In some cases, the force means caninclude a spring, a cable, a bladder, a weight, and the like. The forcemeans can be coupled with an upstream side of the filter, a downstreamside of the filter, or an upstream side of the filter and a downstreamside of the filter. The filter can include a membrane surface that isdifficult for the particulate to adhere.

In still another aspect, embodiments of the present invention encompassa method for removing a particulate from a fluid stream. The method caninclude flowing the fluid stream through a first self-cleaning fluidfilter to capture a first portion of the particulate from the fluidstream, stopping the fluid stream flow through the first fluid filterwhile flowing the fluid stream through a second self-cleaning fluidfilter to capture a second portion of the particulate from the fluidstream, discharging the first captured portion of particulate from thefirst fluid filter, stopping the fluid stream flow through the secondfilter, and discharging the second captured portion of particulate fromthe second fluid filter. In some cases, the first and second capturedportions of particulates are discharged continuously, semi continuously,or non-continuously. The method can also include identifying an uncleanself cleaning fluid filter with a differential pressure sensor. Themethod can also include determining a frequency of a cleaning cycle witha differential pressure sensor. In some cases, discharging a firstcaptured portion of particulate from a first fluid filter includescollapsing the first fluid filter to distort an interior surfacethereof. In some cases, discharging a first captured portion ofparticulate from a first fluid filter includes applying a force to thefluid filter sufficient to convert the fluid filter from an expandedstate to an inverted state. Method embodiments may also include flowingthe fluid stream through a third self-cleaning fluid filter to capture athird portion of the particulate from the fluid stream, coordinatingoperation of the first, second, and third self-cleaning fluid filters,and executing a cleaning cycle that involves only a portion of thefirst, second, and third self-cleaning fluid filters.

In another aspect, embodiments of the present invention provide aprocess for removing a particulate from a fluid stream. The process caninclude controlling the flow of a fluid containing particulates througha fluid permeable, flexible filter, depositing the particulates on theinterior surface of the expanded filter, and expanding the filter bycreating a pressure differential across the filter. The process can alsoinclude extracting energy from the flowing fluid stream and storing theenergy in a mechanical form, controlling the release of the storedmechanical energy so as to apply a collapsing force on the filter,collapsing the filter such that interior surfaces face outward byreducing the pressure differential and applying a collapsing force tothe filter, distorting the filter during the collapse to dislodge thedeposits of the particulates, and removing the dislodged particulates.In some aspects, the flow of fluid is controlled by a valve located onthe inlet piping, the outlet piping, valves located on both the inletand the outlet of the piping, pumps, compressors, or blowers.

In one aspect, embodiments of the present invention provide aself-cleaning, inflatable filter for removing particulates from a fluidstream. The apparatus can include, a fluid-permeable, flexible filterattached to a tube sheet or bulkhead, such that a fluid containingparticulates is forced to flow through the filter. The apparatus canalso include means to cause the fluid containing the particulates toflow through the filter such that fluid pressure expands the filteroutward in the downstream direction, and means to deposit the particleson the interior surfaces of the outwardly expanded filter. The filtercan have material properties to withstand the stresses generated byexpansion and collapsing forces acting on the filter. The filter canalso be free of any physical support structure during expansion otherthan its attachment to the tube sheet. The filter can also be free ofphysical support during collapse, other than its attachment at the tubesheet. In some cases, the apparatus also includes means to extractenergy from the flowing fluid stream and to store the energy in amechanical form, and means to release the stored mechanical energy toapply a collapsing force to the filter in a direction opposite thedirection of the flowing fluid and sufficient to collapse the filterinto an inverted state. The force acting to distort the flexible filteris typically sufficient to dislodge the deposited particulates. Theapparatus can also include a container to receive the particulatesdislodged from the filter and to store the particulates in a manner soas not to disturb the flow of the fluid, and means to remove thedislodged particulates from the container. In some aspects, the means toapply force, or forces, acting on the filter include one or moresprings, cables, bladders or weights. In some aspects, the force meansis attached with an upstream side of the filter, a downstream side ofthe filter, or both. The force acting on the filter can be on theupstream side of the filter, the downstream side of the filter, or onboth sides of the filter simultaneously. The dislodged particulate canbe removed from the filter housing continuously, semi-continuously, ornon-continuously. The semi-permeable filter material can include amembrane to filter out extremely small particles while providing asurface that is difficult for particles to adhere.

In still another aspect, embodiments of the present invention provide asystem for removing particulates from a fluid stream. The system caninclude multiple self-cleaning fluid filters arranged to allowcontinuous filtering operation by reducing the flow of fluid to afraction of the filters, allowing the fraction of the filters toself-clean, and then returning flow to the fraction of cleaned filters.In some cases, a single filter can be taken off line by stopping fluidflow through the filter. In some cases, two, or more, the filters can betaken off line by stopping fluid flow through the filters. The dislodgedparticulate can be removed from the multiple filters continuously,semi-continuously, or non-continuously. In some cases, the systemincludes one or more differential pressure sensors to determine thepressure drop across the filter, which can be used to determine thefrequency of the cleaning cycle. In some cases, more than two filtersare operated as a unit and are put through cleaning cycles that involveonly a fraction of the filters at a time.

For a fuller understanding of the nature and advantages of the presentinvention, reference should be had to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a vertical section of a single filter having a fullyinflated filter bag according to embodiments of the present invention.

FIG. 2 illustrates a vertical section of a single filter having apartially deflated filter bag and accumulated particulates falling tothe bottom of the chamber according to embodiments of the presentinvention.

FIG. 3 shows a vertical section of a filter depicting distortion of afilter bag during deflation and removal of accumulated particulatesaccording to embodiments of the present invention.

FIG. 4 shows a vertical section of a single filter having a fullydeflated, cleaned filter bag and a shed particulate material in alocation for easy removal according to embodiments of the presentinvention.

FIG. 5 illustrates a vertical section of four filters showing threeon-line accumulating particulates, a fourth off-line for cleaning, andparticulates being removed to an external repository according toembodiments of the present invention.

FIGS. 6A and 6B illustrate a four-filter module according to embodimentsof the present invention.

FIG. 6C shows a close-up of a safety filter according to embodiments ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention encompass systems and methods thatallow an inflated filter to slowly deflate and to gently turn itselfinside out after the flow of fluid is significantly reduced oreliminated completely.

Some current filter techniques rely upon water scrubbing to removeresidual fine particles from fluids such as hot gases. Typically, thewater used for scrubbing is in the form of a mist. Unfortunately, thesescrubbing mists can be themselves difficult to remove from the fluidstream. The use of water scrubbing may also create a waste-waterdisposal problem. Coalescing filters are often used to remove these finematerials and mists by Brownian motion, but can introduce a significant,undesirable pressure drop to the system. In some cases the capturedparticles may not be washed off the coalescing filter by the capturedmists, and the coalescing filters may require periodic service to removethe captured particles, or the coalescing filters may need replacement.

Some current approaches use either cloth filters supported by an openstructure or cage, or cloth filters that are unsupported and inflated bythe pressure differential across them. Filtering with unsupported filtermedia often uses mechanical shaking of the filter bag to dislodge thefilter cake after stopping fluid flow to the filter bag; however, thismechanical shaking can be inefficient and the filters may tend to plugmore often. The mechanical shaking can introduce stresses in the filtermedia due to the whipping action imparted. Static sand filters oftenhave a problem with cleanup, since the particles removed are embedded inthe sand, and the volume of material to be removed is substantiallygreater than the volume of particulates captured. Sand filters with thepotential for periodic back flushing typically involve relativelycomplicated piping and valving. Centrifugal separators for removingsmaller, lighter weight particles can be exceedingly complex, and powerintensive. In addition to a substantial initial investment, operatingand maintenance costs can be quite high for a centrifugal filtrationapparatus.

In some current approaches, a longitudinal filter bag is prevented fromfully collapsing by a central, axial support, thereby preventing thefull cleaning or cleaning of particles from a range of liquids. Suchsystems are complex and costly. Some approaches involving a bag supportmay involve a filter area in contact with a solid surface, thusdecreasing the filtering function. Moreover, some current bag supportsdo not provide sufficient bag distortion to adequately loosen anddislodge filter cake, which may be problematic when filtering very fineparticles or sticky particles that are difficult to remove from thefilter surface. Other current approaches require a scraper, brush, orpressurized fluid to dislodge accumulated filter cake. In someapproaches, pulses of pressurized fluid are back pulsed through one ormore of the bags to reverse the fluid flow through the bag and dislodgethe accumulated filter cake. Such back pulsing can harm filter elements,and the ingress of an oxidizing agent is hazardous if the pulsed fluidis combustible.

Embodiments of the present invention provide filters that use no bagsupports, scrapers, brushes, or nozzles to dislodge the filter cake. Insome cases, the surface area available for filtering increases as thebag is expanded and it does not make contact with any solid surfacesupport during filtration, making all or most of the filter's surfacearea usable. Fluid flow can be through the open end of a bag and outthrough a fabric. Embodiments provided herein are well suited for use inrural areas, as well as in developing countries. Filter systemembodiments of the present invention can have minimal need for equipmentsuch as back pulsing pumps, rate controllers, and air compressors. Theymay have little or no dependence upon outside power sources. Theseapproaches to remove the filter cake from the filter media are typicallyvery gentle and efficient. Filter embodiments of the present inventionare well suited for use with biomass power generation systems andmethods, such as those described in commonly owned U.S. patentapplication Ser. No. ______, filed Jun. 28, 2006 (“Method and Apparatusfor Automated, Modular, Biomass Power Generation,” Attorney Docket No.026353-000300US), the entire contents of which are incorporated hereinby reference.

Turning now to the drawings, FIG. 1 illustrates a vertical section of asingle filter having a fully inflated filter bag according toembodiments of the present invention. A weight 101 is attached to theinside center of a closed end of a bag 103. A flowing fluid 110 withentrained particulates enters the filter housing, for example via aninput or entry piping, below the inflated filter bag 103 and travels inan upward direction. Flowing fluid 110 passes through the filter bag 103and exits as a clean fluid 111, for example through an exit or outletpiping. In some embodiments, weight 101 is light enough to allow thefilter bag 103 to inflate with a modest pressure differential(dP=P₁−P₂), but heavy enough to ensure that the bag turns itself insideout in a symmetric manner during deflation as shown in FIG. 2, ratherthan falling off to one side. FIG. 2 illustrates a vertical section of asingle filter having a partially deflated filter bag and accumulatedparticulates falling to the bottom of the chamber according toembodiments of the present invention.

FIG. 3 shows a vertical section of a filter depicting how the distortionof the filter bag during deflation is able to remove accumulatedparticulates. A curved upwardly facing shape 102, which may include aregion of maximum or extreme filter distortion, can form at the top edgeof the bag upon deflation. The curved region of maximum filterdistortion will travel slowly downward until the bag has fully deflatedas shown in FIG. 4. As the region of maximum filter distortion 102encounters new supplies of deposited particulate 109, the deformation ofthe filter surface is sufficient to dislodge accumulated particulate 100from the bag surface.

In one non-limiting embodiment, a five-pound (2.3 kg) weight is usedwith an 18-inch diameter filter bag. This weight may include a single ormultiple objects for each filter bag. Although FIG. 2 shows the weight101 hanging from the inner, upstream, side of the bag, it may also beattached to the outer, downstream side of the bag. Other non-limitingembodiments would use a spring or cable to apply deflating force orforces to the filter bag.

To deflate the filter bag for cleaning, a valve 105 in the exit pipingis closed thereby stopping flow of the fluid 110 eliminating theinflation forces resulting from the differential pressure across the bag103. Alternatively, the valve may be placed in the inlet piping, or inboth the inlet and the outlet piping. As shown in FIG. 2, when thedownstream pressure P₂ approaches P₁, the weight 101 pulls the filterdownwardly, the deflating filter is turned inside out, and the filtercake 109 is dislodged. The falling dislodged filter cake 100 falls to alocation 108 that is free from disturbance by the flow of fluid thatresumes when valve 105 is later re-opened. The accumulated, dislodgedfilter cake 122 accumulates in the bottom of the filter housing 108.

Non-limiting examples of the exit valve 105 include ball valves, gatevalves, and the like. Inexpensive butterfly valves are adequate tocreate the desired deflation. The seal in the valve 105 may allow someleakage of the fluid and still deflate the filter bag sufficiently forcleaning.

The dislodging of the filter cake is shown in more detail in FIG. 3. Asthe filter bag is flexed and turned inside out, the filter cake 109 isdeformed and broken up. The broken pieces of filter cake 100 fall fromthe bag 103. Also shown in FIG. 3 in more detail is the external lip 112formed by a tube or rod welded to the short cylinder 107, which in turnis welded to the tube sheet 106. Alternatively, the lip could be formedby swaging the top of the short cylinder 107. The external lip 112 onthe short cylinder 107 prevents the band clamp 104 from easily slidingoff. In addition, a thick drawstring 113 in the filter bag aids ininstallation of the band clamp 104 and further aids in preventing thebag from easily slipping under the band clamp 104 and off the shortcylinder 107. The combination of the external lip 112 and the thick drawstring 113 provide for a very secure attachment of the filter bag 103 tothe tube sheet 106, without excessive tightening of the band clamp 104that could damage the filter bag.

FIG. 4 shows a vertical section of a single filter having a fullydeflated, cleaned filter bag and the shed particulate material in alocation for easy removal. After a suitable time interval to allow thebag to fully deflate, the pressure on the inside, upstream side of thebag P₁ is about equal to the pressure on the outside, downstream side ofthe bag P₂. Then, the valve 105 is opened and fluid flow started throughthe cleaned bag to inflate it again, as shown in FIG. 1. Then anotherone of a series of filter bags is taken off line as shown in FIG. 5 byshutting its valve to deflate it to remove its accumulated char cake.FIG. 5 shows a vertical section of four filters having three on-lineaccumulating particulates, a fourth off-line for cleaning, andparticulates being removed to an external repository. Upon cleaning, thefilter is returned to service. This sequence is repeated with eachfilter bag, so that all filter bags are periodically cleaned. During thecleaning cycle, the filters not being cleaned are available for processfiltering. FIG. 5 also shows that after the filter cake 109 is dislodgedfrom the filter bag 103, it falls into a common bin 114, where therecovered particulate material 122 may be removed intermittently orcontinuously with a series of augers 115 and 116 (or other conveyingdevice) that are rotated by motors 117 and 118 respectively. Theparticulate is removed to a drum 119 for disposal or sale. Bytemporarily stopping the augers 115 and 116 and closing valve 123, theparticulate storage drum 119 may be removed from the system withoutinterrupting the flow of fluid through the system. After a newparticulate storage drum is installed, the valve 123 is opened and theaugers 115 and 116 restarted to remove the accumulated particulates.

The filter media in a non-limiting embodiment is a thin, flexiblematerial that may have a membrane attached to its upstream surface toachieve relatively complete removal of even very fine particles. Anon-limiting embodiment of this filter material has a PTFE membraneattached to a 6-oz/yd² woven polyester cloth. This slick, non-stickmembrane provides extremely good filtration of very fine particles,which are held in place by the fluids passing through the accumulatedfilter cake. This filter material is rated at 135° C. (275° F.) forcontinuous duty and 149° C. (300° F.) for a maximum surge temperature.The filter cake has difficulty adhering to the slick surface of themembrane attached to the filter cloth, facilitating the removal ofaccumulated filter cake. Condensation of moisture on the filter mediacan severely blind the filter. To avoid this condensation of moisture,the filter housing can be fitted with electrical resistance heaters.These heaters maintain the filters above the dew point of the fluid tobe filtered, as needed.

Multiple Filter Bags

Cleaning of the filter bags can lend itself to automatic control veryeasily, which can be based upon a timer, or upon the pressuredifferential across the filter. A non-limiting embodiment of this systemuses five such filter bags, each of which are individually cleaned forten minutes once every fifty minutes when the pressure drop exceeds aselected value. Embodiments of the present invention have been shown todeliver extremely clean gas from a biomass gasification system withoutthe need for liquid scrubbing systems, e.g. <10 ppm tars and <1 ppmparticulates after filtration, based on a gas sampling protocol asdiscussed in Diebold, et al. “The BioMax® 15: The Automation,Integration, and Pre-commercial Testing of an Advanced Down-DraftGasifier and Engine/Gen Set,” Proceedings of the Conference Science inThermal and Chemical Biomass Conversion, A. V. Bridgwater, ed.,Victoria, B. C. Aug. 30-Sep. 2 (2004), the contents of which are herebyincorporated by reference for all purposes.

FIGS. 6A and 6B illustrate a four-filter module, and FIG. 6C shows aclose-up of a safety filter, according to embodiments of the presentinvention. Safety filters are useful for preventing or minimizingproblems when an original filter ruptures. In some embodiments, eachfilter bag is 18 inches in diameter and 30 inches long. Multiple,cylindrical filters are employed so that the exiting fluid flow fromeach filter can be individually shut off by activating a suitableactuator to close a butterfly valve 105 and the accumulated filter cakeis dislodged and removed automatically as shown in FIGS. 1-5. The upperfilter housing surrounding each bag is an inverted 55-gallon drum 120.The entire filter assembly can be enclosed by insulated panels attachedto supporting structures 124. Excessive heat in the insulated enclosurecan be removed with a fan 125.

The filter bags often do not require periodic maintenance. However, inthe event they need to be inspected, cleaned, or replaced, the 55-gallondrum 120 surrounding each filter bag can be easily removed with a drumclamp. The large diameter band clamp, holding the filter bag to the veryshort cylinder attached to the tube sheet, is then accessible and thebag can be readily removed.

The fluid with entrained particulate enters the system through a pipe126 and is split into four streams by a primary tee or “Y” 127 and twosecondary tees or “Y's” 128. Each stream enters tangentially into eachof the cylindrical filter housings, below the filter bag. Thesetangential entries separate the larger particles from the fluid and theentrained smaller particles. This filter system employs cylindricalfilters that are inflated by the pressure differential across the filtermedia. This unsupported filter-bag design can eliminate the need forexpensive metal support structures, or cages, for the filter bags.

After the filter cake is dislodged from the filter bag, it falls into acommon bin 114, where the recovered particulates may be temporarilystored, or intermittently or continuously removed with an auger system115 and 116, through a valve 123 to fall into a drum 119 for disposal,use, or sale. Rupture disks 131 are located on the lid of drum 119 andalso on the common bin 114 to relieve any excessive pressure, e.g., froman explosion, that could damage the equipment. A level sensor 132 on thelid of the drum 119 sends a signal to the operator that the drum isfull. Inspection ports 133 using easily removed flanges (e.g., sanitaryfittings) are located at each end of the common bin 114. Individualsecondary or safety filters 134 are located downstream of each filterbag. The clean fluid exits the filter assembly at 135, after passingthrough a flow meter 136. A pair of pressure transducers or adifferential pressure transducer monitors the pressure drop across thefilter assembly. A safety filter may be located downstream of thefiltering apparatus. In the event of a filter bag rupture, the safetyfilter will rapidly become blinded, effectively isolating and removingthe ruptured filter bag from the process without allowing fines to passdownstream.

High Length to Diameter Ratio: Example

To increase the surface area for filtering, in some embodiments it canbe advantageous to use many smaller diameter filter bags, rather than asingle large diameter filter bag of the same length. To demonstrate thephysical movement of this filter in a relatively smaller diameter, a4-inch diameter filter bag by 30 inches long was fabricated of the samelight-weight 6-oz/yd² filter material with a PTFE membrane, as was usedfor the 18-inch diameter by 30-inch long filter bags. A 1-lb weight wasattached to the inside of the circular, closed end of the 4-inchdiameter bag. This small diameter bag was attached to the outside of along 4-inch metal tube with a worm-gear hose clamp. A large shop vacuumcleaner was used to blow air into the filter bag to inflate it and liftthe weight. When the vacuum cleaner was shut off, the filter bag turneditself inside out in a manner similar to the larger diameter bag havingthe same length. The single, smaller diameter filter bag had a slighttendency to fall to one side before it completed its inside-out maneuverto end up inside the 4-inch diameter metal tube. In the application ofmultiple, smaller diameter filter bags in a cylindrical bag house, thebags can be clustered together and hold each other up to prevent eachother from falling to one side, while they deflate and dislodge thefilter cake. Thus, the use of relatively long filter bags to increasethe filter surface area in a given size of filter housing is feasiblewith this self-cleaning concept.

Although certain system, device, and method embodiments have beendisclosed herein, it will be apparent from the foregoing disclosure tothose skilled in the art that variations, modifications, alternativeconstructions, and equivalents of such embodiments may be made withoutdeparting from the true spirit and scope of the invention. Therefore,the above description should not be taken as limiting the scope of theinvention which is defined by the appended claims.

1. A process for removing a particulate from a fluid stream, comprising:flowing a fluid stream containing a particulate through a fluidpermeable, flexible filter; expanding the filter and depositing theparticulate on an interior surface of the expanded filter; discontinuingthe flow of the fluid stream through the filter; collapsing the filterto distort the interior surface; and dislodging the particulate from thedistorted interior surface of the filter.
 2. The process of claim 1,wherein expanding the filter comprises creating or increasing a pressuredifferential across the filter.
 3. The process of claim 2, whereincollapsing the filter comprises removing or reducing the pressuredifferential across the filter.
 4. The process of claim 1, whereinexpanding the filter comprises extracting an energy from the fluidstream and storing the energy in a mechanical form.
 5. The process ofclaim 4, wherein collapsing the filter comprises releasing the storedmechanical energy.
 6. The process of claim 1, wherein flowing the fluidstream comprises controlling the fluid stream with a fluid control meansdisposed upstream of the filter, the fluid control means selected fromthe group consisting of a valve, a pump, a compressor, and a blower. 7.The process of claim 1, wherein flowing the fluid stream comprisescontrolling the fluid stream with a fluid control means disposeddownstream of the filter, the fluid control means selected from thegroup consisting of a valve, a pump, a compressor, and a blower.
 8. Aself-cleaning filter apparatus for removing a particulate from a fluidstream, comprising: a fluid-permeable, flexible filter having anexpanded state and an inverted state, the expanded state adapted tocapture the particulate on an interior surface of the filter whenreceiving the fluid stream therethrough, and the inverted state adaptedto dislodge the particulate from the interior surface; a force meansconfigured to apply a force to the filter sufficient to convert thefilter from the expanded state to the inverted state.
 9. The apparatusof claim 8, wherein the force means is configured to extract an energyfrom the flowing fluid stream as it passes through the filter, to storethe energy in a mechanical form, and to release the stored mechanicalenergy to apply the force to the filter.
 10. The apparatus of claim 8,wherein the filter is coupled with a tube sheet.
 11. The apparatus ofclaim 10, wherein the filter is free of any physical support structure,other than the tube sheet and the force means.
 12. The apparatus ofclaim 8, wherein the force means comprises a member selected from thegroup consisting of a spring, a cable, a bladder, and a weight.
 13. Theapparatus of claim 8, wherein the force means is coupled with anupstream side of the filter, a downstream side of the filter, or anupstream side of the filter and a downstream side of the filter.
 14. Theapparatus of claim 8, wherein the filter comprises a membrane surfacethat is difficult for the particulate to adhere.
 15. A method forremoving a particulate from a fluid stream, comprising: flowing thefluid stream through a first self-cleaning fluid filter to capture afirst portion of the particulate from the fluid stream; stopping thefluid stream flow through the first fluid filter while flowing the fluidstream through a second self-cleaning fluid filter to capture a secondportion of the particulate from the fluid stream; discharging the firstcaptured portion of particulate from the first fluid filter; stoppingthe fluid stream flow through the second filter; and discharging thesecond captured portion of particulate from the second fluid filter. 16.The method of claim 15, wherein the first and second captured portionsof particulates are discharged continuously, semi-continuously, ornon-continuously.
 17. The method of claim 15, comprising identifying anunclean self-cleaning fluid filter with a differential pressure sensor.18. The method of claim 15, comprising determining a frequency of acleaning cycle with a differential pressure sensor.
 19. The method ofclaim 15, wherein discharging the first captured portion of particulatefrom the first fluid filter comprises collapsing the first fluid filterto distort an interior surface thereof.
 20. The method of claim 15,wherein discharging the first captured portion of particulate from thefirst fluid filter comprises applying a force to the fluid filtersufficient to convert the fluid filter from an expanded state to aninverted state.
 21. The method of claim 15, further comprising: flowingthe fluid stream through a third self-cleaning fluid filter to capture athird portion of the particulate from the fluid stream; coordinatingoperation of the first, second, and third self-cleaning fluid filters;and executing a cleaning cycle that involves only a portion of thefirst, second, and third self-cleaning fluid filters.